Risk you'll have to take?
I don't know, I'm still new to the game, but these cards look useless against certain opponents;
almost useless against rainbow decks
useless against decks with no permanent control
useless against decks with no way to poison you (when considering the shard of gratitude and other healers are much better substitutes)
less useful against darkness and death decks
Anyways, use against the opponent is kind of just an extra, the real use would be using it on your own creatures.